No. I.] THE CRANIAL NERVES OF AMPHIBIA. 1 05 



Lithium Bichromate Modification for Adult Brains. — I have 

 made a number of attempts to dispense with osmic acid in 

 the fixing fluid, but without success for the tadpole. A modifi- 

 cation was discovered, however, which gives some very fine 

 impregnations in the adult mammalian cerebrum and cerebel- 

 lum, dispensing with osmic acid and yet requiring only a few 

 days for the process. It consists simply in the use of lithiwm 

 bichromate instead of potassium bichromate. This salt is very 

 soluble in water and makes a solution somewhat darker than 

 the potassium bichromate, which it resembles. It hardens very 

 much more rapidly than the latter, so that small pieces of brain 

 placed in a 3^ solution require only a day or two instead of 

 20 to 30 days to reach the condition favorable for impregna- 

 tion. This favorable condition, however, is passed through very 

 quickly. I have not had opportunity, as yet, to test this 

 method thoroughly, but have obtained splendid pictures of the 

 Purkinje and pyramid cells, and also in the fowl's brain of the 

 granule cells, showing the -["-shaped division of their axis 

 cylinders in the molecular layer of the cerebellum. 



Sodium Sulphate Modification for Increased Penetration. — 

 One of the defects of the Golgi method, especially of the 

 rapid method, seems to lie in the poor penetration of the silver 

 nitrate, resulting in irregular and defective impregnations. It 

 occurred to me that by combining the silver solution with some 

 salt that would be indifferent chemically in the reduction of 

 the silver, but would facilitate its penetration, the results might 

 be improved. Two salts were tried, namely, sodium sulphate 

 and zinc sulphate. Both seemed to tend to produce the 

 desired effect, for some of the best and most thorough impreg- 

 nations were obtained from specimens treated especially by the 

 former. The mixture of silver nitrate and the sodium sulphate 

 was made in varying proportions. In two of the most suc- 

 cessful impregnations the following were the solutions into 

 which the objects were brought from the osmium-bichromate 

 mixture: (i) Sodium sulphate 6J0 i vol. -f- silver nitrate 4^ 

 I vol.; (2) sodium sulphate 8^ i vol. + silver nitrate ijo i vol. 

 A precipitate is formed in mixing these, and it would be 

 advisable to so adjust the proportions as to prevent this. 



